European Patent Application No. EP-A-0125691 describes such an image detector in which the photodetector array is provided as a matrix of photosensitive diodes or photodiodes and associated thin-film circuitry on one major surface of an insulative substrate and the electromagnetic radiation conversion layer is provided as a layer of phosphor material dispersed in a binder on the other surface of the insulative substrate. Such an arrangement requires that the insulative substrate be transparent to the outgoing radiation emitted by the electromagnetic radiation conversion layer. Moreover, it requires that the processing technology used to provide the phosphor layer be compatible with that used to form the photodetector array and, for example, the processing temperatures which can be withstood by amorphous silicon thin film circuits lie at the lowermost end of the deposition temperature range for phosphors such as caesium iodide.